Internal combustion engines generate exhaust as a by-product of fuel combustion within the engines. Engine exhaust contains, among other things, unburnt fuel, particulate matter such as soot, and gases such as carbon monoxide and NOx. To comply with regulatory emissions control requirements, it is desirable to reduce the amount of unburnt fuel, soot, and other gases in the engine exhaust. Due to the rising cost of liquid fuel (e.g. diesel fuel) and to comply with the emissions control requirements, engine manufacturers have developed dual-fuel engines and/or gaseous-fuel engines.
In these engines, using a lower-cost fuel, for example, a gaseous fuel together with or without liquid fuel helps improve the cost efficiency of the engine. Use of gaseous fuel to fully or partially replace the traditional liquid fuels such as, gasoline or diesel fuel, may also help to lower the amount of soot and/or other undesirable gases in the exhaust. To comply with increasingly stringent emissions control regulations, these engines may be operated with a lean air-fuel ratio, which may prevent the fuel from being fully burned within the combustion chamber.
Incomplete combustion of the fuel may result in the formation of undesirable amounts of unburned hydrocarbons and NOx. Further, any fuel that remains unburnt and escapes from the combustion chambers does not participate in combustion, reducing the thermal efficiency of the engine. The escaping unburnt fuel also contributes to the total amount of undesirable emissions produced by the engine. Although the unburnt fuel and NOx may be removed from the exhaust in one or more after-treatment devices, implementing these devices adds to the cost of operating the engine. Therefore, it is desirable to reduce the amount of unburnt fuel and NOx in the exhaust leaving the combustion chamber.
One technique for improving combustion of the fuel in the combustion chamber is disclosed in U.S. Pat. No. 8,783,229 B2 to Kim et al. (“the '229 patent”) that issued on Jul. 22, 2014. The '229 patent discloses a gaseous fuel internal combustion engine that includes a gaseous fuel delivery mechanism and a distributed ignition promoting mechanism. The ignition promotion mechanism includes a bead presentation device configured to present a liquid bead of ignition promoting material such as engine lubricating oil. The '229 patent explains that during operation, gases passing through the intake passage dislodge the liquid bead from the bead presentation device and carry the ignition promoting material into the cylinder. The ignition promoting material distributed within the cylinder ignites, helping to ensure combustion of the gaseous fuel in the combustion chamber. The '229 patent discloses that rather than attempting to inject the ignition promoting material into the intake passage, the system of the '229 patent relies on the intake gases to dislodge and distribute the ignition promoting material in the combustion chamber.
Although the '229 patent discloses the use of lubricating oil beads to promote combustion of gaseous fuel in the combustion chamber, the disclosed method may be improved further. In particular, the method of the '229 patent does not control the number of droplets of the lubricating oil or the droplet size of the oil droplets that enter the combustion chamber with the intake gases. Adding too little of the lubricating oil or inadequately distributing the lubricating oil within the combustion chamber may not be sufficient to burn the fuel in the combustion chamber. Adding too much lubricating oil may increase consumption of the lubricating oil and may also result in an increase in particulate matter generation because of the combustion of the excess lubricating oil in the combustion chamber.
The engine system of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.